1. Field of the Invention
The invention relates to a vehicle and a method of controlling the vehicle, and particularly relates to a vehicle on which an engine and an electric motor connected to the engine via a gear are installed, and a method of controlling the vehicle.
2. Description of Related Art
Hybrid vehicles on each of which an electric motor serving as a driving power source is installed in addition to an engine have been marketed. Part of the hybrid vehicles may be classified as one type of electric vehicles. In the hybrid vehicle, the engine and the electric motor are connected to each other via a planetary gear, for example.
When the output torque of the electric motor is in the vicinity of zero in the hybrid vehicle in which the engine and the electric motor are connected via a gear, the gear may vibrate because of the output torque of the engine, and tooth surfaces of the gear may repeatedly collide with each other. In this case, sound may be generated from the gear, and the sound may cause a passenger of the vehicle to feel uncomfortable.
In paragraph [0041] of Japanese Patent Application Publication No. 2009-173125 (JP 2009-173125 A), it is described that, in, order to solve the above-described problem, an operating point of the engine is set during load operation of the engine, based on an operating line that makes it possible to suppress occurrence of abnormal sound in the gear. It is also described in paragraph [0043] of JP 2009-173125 A that, in order to reduce the amount of change of the engine speed when the engine shifts from independent (no-load or idle) operation to load operation, the engine is operated under no load, or independently, at the lowest rotational speed of the operating line, on which it is possible to suppress occurrence of abnormal sound in the gear.
When the engine is in a motored state (in which the output shaft of the engine is rotated while ignition is stopped), no torque is transmitted from the engine to the gear; therefore, sound generated from the gear between the engine and the electric motor is small. However, when the engine shifts from the motored state to a state in which the engine operates under a load, the output torque of the engine becomes excessively large for a moment, and sound may be generated from the gear, via which the engine and the electric motor are connected to each other. This situation is not considered nor addressed at all in JP 2009-173125 A.